The present invention generally relates to image forming apparatuses, and more particularly to an image forming apparatus which forms a multi-color (color) image on a medium such as paper.
An electrophotography type image forming apparatus which transfers a toner image on a medium is applied to printers, copying machines, facsimile machines and the like. Recently, image forming apparatuses which form color images have become popular.
Generally, as shown in FIG. 1, a color printer 100 is connected to a host computer 110 which is provided as a host unit, and the color printer 100 makes a color printing with respect to predetermined paper by receiving data from the host computer 110.
Normally, the printer 100 includes a color printing mechanism engine 101, a duplex unit 102, hoppers 103 and 104, a cassette 105, a tray 106, a stacker 107 and an operation panel 108.
The color printing mechanism engine 101 forms a mechanism for making the color printing with respect to the predetermined paper, and the duplex unit 102 forms a mechanism for making a duplex printing with respect to the predetermined paper.
The hoppers 13 and 14 store plain paper of predetermined sizes as printing paper. The cassette 105 stores color paper that is supplied after a print job is completed and before a next print job is started, so as to distinguish the print jobs. Printed paper are ejected onto the tray 106 and the stacker 107.
The operation panel 108 includes control keys and switches for inputting various instructions with respect to the printer 100, a display for displaying the operating state of the printer 100, and the like. In FIG. 1, a main console 111 is provided on the host computer 110. This main console 111 is provided with control keys, switches, a display and the like, and this main console 111 is used when an operator needs to monitor or intervene with the operation of the host computer 110.
As shown in FIG. 2, the color printing mechanism engine 101 is made up of four color printing units 111Y, 111M, 111C and 111K. The color printing units 111Y, 111M, 111C and 111K are respectively provided to carry out the printing using a corresponding one of the colors which are yellow (Y), magenta (M), cyan (C) and black (K). Each of the color printing units 111Y, 111M, 111C and 111K has a developing unit 112, a photoconductive body or drum 113, an optical unit 114 and a transfer roller 115.
The developing unit 112, the photoconductive drum 113, the optical unit 114 and the transfer roller 115 which form each of the color printing units 111Y, 111M, 111C and 111K are extremely well known, and a detailed description thereof will be omitted.
A reference numeral 116 denotes a fixing unit, and a reference numeral 117 denotes a paper transport path.
In the color printing mechanism engine 101 having the construction shown in FIG. 2, the paper supplied from the hopper 103 or 104 is transported from the color printing unit 111Y towards the color printing unit 111K along the paper transport path 117, and toner of a corresponding color is transferred onto the paper by each of the color printing units 111Y, 111M, 111C and 111K. The toner transferred onto the paper is fixed by the fixing unit 116, thereby making the color printing.
However, according to the color printer 100 provided with the color printing units 111Y, 111M, 111C and 111K described above, all of the color printing units 111Y, 111M, 111C and 111K are always operated even when carrying out the printing using a single color. For this reason, the photoconductive drum 113 of the color printing unit which is not frequently used wears out and a developing agent used in this color printing unit deteriorates, thereby causing a problem in that the color printing unit which is not used frequently has a short serviceable life.
In addition, because the color printing unit which is not used is also operated simultaneously as the other color printing units which are used, there are problems in that unnecessary power is consumed, and residual toner on the photoconductive drum 113 of the color printing unit which is not used adheres onto the paper as stain, thereby deteriorating the printing quality.